Concept:A mirage involves both refraction and total internal reflection of light.
Explanation:On hot days, the air near the ground is hotter and less dense than the air above.
As a result, the refractive index of air decreases towards the ground.
Light from a tall object (like a tree) passes through layers of air with decreasing refractive index.
Due to this variation, the light ray bends away from the normal — this is refraction.
If the ray strikes the ground-level air at an angle greater than the critical angle, it undergoes total internal reflection.
To a distant observer, the reflected light appears to come from below the ground, creating the illusion of water on the road.
Thus, a mirage is formed due to both refraction (gradual bending) and total internal reflection (at the ground layer).
Answer:Option D: both refraction and total internal reflection of light.
